Cavity resonator magnetron



Jan. 8, 1952 w. E. WILLSHAW CAVITY RESONATOR MAGNETRON Fild Aug. e, 1947Patente-2d Jan. 8, 1952 CAVI'EY RESONATOR MAGNETRON Wiiiiam ErnestWilishaw, Kenton, England, as-

signozr t0 The M-O Valve Company Limited,

Landau, Eingland Appliczwtionlngus 6, 1947, Serial N01, 766,756 InGreat-Britasin May 171946 Secaion 1, Puh'ic Law 690, August 8, 1946Pa's-encaxpistes May 17, 1956 6 Chinas. 1

This. invention relaces 150 apparatus f0r am" plifying or multiplyingthe frequency of electrical oscillations 0f high frequeney, espgciallybut not exclusively, of frequency as high as er higlzer than 3000megacycles per second.

One of the most efiective forms of appai*atus Which. has been developedfor generating electrical. oscillations of' very high frequency is themagnetron escillator, and the object of this inventionis to adapt for'she purpose cf ampl'ifying and. frequency multiplying, flne principles021 which the magnetron depends .for the generation o1 oscillations.

In the we1l known magnetron oscillator in which a cylindrical cathode issurrounded by a ring of hollow res'onators, energy is transferred fromd'ireet current fiel'd to an oscillatory fie1d. by the reaction ofelectrons energised by the direct oz:urrent fieldwith the oscillatoryfields Withitn.

the hollow resonators a magnetio fie1d app1ied transversely of thedirect current fiel d ensuring that electrons which receive energy fromthe oscillatory fie1ds are immediacely returned so the cathode whereaselectronswhich give up energy to the oscillatory fie1ds trave1 round thecathod in synchronism With a potential wave travelling round theresonators so that these electrons give up energy to a plura1ity ofresonators in succession.

According 110 the present invention a magfor density modulating saidstream in acc0rdance with the amplitude and frequency cf Ehe inputoscillation, electrod'es defining an electron orbit space along whichsaid density mndulated stream can fiow under the influence 033 anelectrostatic field between sa.id electrodes amd a transverse magneticfield, a. plurality of coupled resonant output circuits spaced apartalong said electrrm orbit. space so as 130 Tue excitable in successionby said density modulated. stream 2md resonant as a whole at a frequencyn f, where n is an integral number and f is the frequency of the said:inm1t oscillation, and means for extracting the required outputoscillation from the said output circuits. For an amplifler n equals oneand for a frequency multiplier n is an integer greater tha,n one. Forfrequency-multiplying the density modulation o1 the electron stream mustbe nonsinusoidal.

The successive excitationof the ou-tput circuits sets up a system ofpotential variation having a travelling wave component which, With theresonanti output circuits spaced in accordance With the mean velocity ofthe. electrons is synchronised With the flow of the electrons so tha.t aconsiderable transfer of energy is obtained and a streng outpu1;oseillation built up.

The term resonant output circuits is used instead of hollow resonatorssince the resonators might in some cases be replaced by resonant fingersor possibly by physically distinct resonant output circuits connectedacross s1its between adjacent anode segments.

In general, and especially for very high frequency use, all theelectrodes and circuits will be enclosed within or form part of theWalls of the evacuated enclosure in which the electrons are adapted tomove, but in some cases parts of the apparatus, and especially parts offihe input and output circuits; may be locat'ed' or extend out'side theWalls of' the enel0sure;

It may also be noted' that' the output circuits need not be individuallyresonant at t11e frequency, er an integral multiple of the frequency, ofthe input oscillaoion so l'ong as the' combined output circuit formed bythe co'upling tcgeher of the individual output circuits is eifectivelyresonant at' the required' output frequency; thus the rising sunarrangement often used in resonant cavity magnetronsmay be adoptedtoensure wicle mode-spacing.

The coupling together of the output circuits Will in general be effectedmerely' by their dis position, but in somecasesspecial couplirigmaatlsmay be used. Thema must, of course, be substantially nocoupling betweenthe oufiput circuits and the input circuit 01" the system may be se1foscillating and not function zus an aniplifier er frequency multiplier.

Further it' may be noted that, with other forms 0f amplifier; theapparatu.s ma=y have utility even if the amplitude cf theoutput oscil-Iation is lass than that of the input oscillation; accordingly it Willbe understood that in; this specification the: term 'amplifying does ntnecessarily i'mp1y that the output' oscillation. is of greater amplitudethan tbe input Gscixllation a1though this Will often be the case.

The preferred method. of producing an densiy modulated stream ofelectrons in apparatus in accordance with the invencion is so arm-rage athermionic cathoe opposite an input circuit which is excitable by andresonant at the fre quency of the input oscillation .s0 that theemission from the cathode: isscontrolled by the inpuo cirouit anct 150arrange: a non-secondarily emissive electron-intercepting electrodeadjacenl; 130 the cathode so that by the applicatlon of crossedelectrostatic and magnetic fields, which may be the same as thoseapplied in the electron orbic space, the electrons emitted from thecathocle are directed to the intercepting eleccrode in the absence ofany input oscillation; then when the input oscillation is appliedelectrons which are retarded by the input circuit are diverted from theintercepting electrode and fiow on to excite the output circuits alongthe electron orbit space, the effect being that isolated groups ofelectrons are released 110 the electron orbit space, the number ofelectrons in each group corresponding to the amplitude of the inputoscillation and the spacing between the groups corresponding to thefrequency of the input oscillation; the spacing between the outputcircuits is arranged 130 be half ehe spacing between the group ofelectrons. This method of density modulation results in anon-sinusoidally modulated stream Which is well suited for frequencymultiplylng.

It Will be appreciated that either amplifying er frequency multiplyingapparatus in accordance With the invention need not be of the circularform simllar to the well known magnetron osclllator; a linear form inwhich the cathode eleo trode and a co-operating anode electrode aresubstantially plane may be usecl; but the clrcular form is preferred andone embodiment of the invention in this form, which is an amplifier,will now be described by way of example with reference to Figures 1 and2 of the accompanying drawing.

Figure 1 shows a section at right angles to the circular axis and Figure2 a section comtaining the circular axis; the section of Figure 2 is inthe plane 22 of Figure 1, looking from the right, and the section ofFigure 1 is in the plane II of Figure 2, also looking from the right.

In this embodiment, the apparatus comprises a cylindrical metal blockanode l recessed als each end face to leave an annular peripheral flange2 and pierced co-axially by a cylindrical hole 3 which provides theelectron orbit space. Around one half of this hole the block ls furtherrecessed deeply ab each and face to form a thinner semicircular rlng 4which is pierced parallel 110 the axis by eight holes 5, eachcommunicating with the hole 3 through a radial slot 6 pieroed throughthe ring 4 parallel 170 the axis, and, each adl'acent to the thickerpart of the block, two semi-circular holes 1 each communicating with thehole 3 through a slot 8 of half the width of the slots 5.

The holes 5 and slots 6 constitute output cavities each resonant at thefrequency at which the apparacus is adapted to operate, that is amplify,and the holes l and slots 8 likewise constitute cavities resonant alsthe said frequency; these last two cavities are shaped so as to havezero field along the face of the thicker part of the block so avoiclcoupling with the input circuit.

Near the centre of the thicker part round the central hole 3, the blockis pierced parallel to the axls by two radial slots 9, each of radiallength effectively one quarter of the wave-leneth at which the apparatusis adapted 130 operate and between the slots the block is recessed fromeach end face toform a wedge-shaped finger lll, resonant at the saidwave-length, having the same axial thickness as the ring 4; the finger10 constitutes the resonant input circuit.

Along the centre of the hole 3 there is located, coaxially, acylindrical cathode electrode II which is carried by clrcular end platesI2 each supported by a stout meoal lead I3 s'ealed through thecylindrical wall of the block by a metal-t0- glass thimble seal I4 inaccordance with the technique usual in magnetrons. The surface of thecathode elecorode II is treated to render it everywhere substantiallynon-secondarily emlssive, Tor example by coating with titanium dioxide.

At about the centre and to one side of the finger I0, the cathodeelectrode l l and end plates l'2 are cut away accommodate an indirectlyheated primary cathode I5 consisting of a metal box containing a heaterI5; the ourved outer face of the box, which face is coated wioh electronemissive material, ellectively forme a 00mpleti0n cf the cathodeelectrode cylinder.

The primary cathode is carried by end plates I! each supportecl by astout metal lead I8 sealed through the cylindrical wall of the block bya metal-to-glass thimble seal l9; the leads 58 serve also as currentsupply leads to the healser I6 and the primary 'cathode is insulateclfrom the cathode electrode so that the two electrodes can if required bemaintained ab different potentials by means of the leads I8, l3respectively.

Between the primary cathode !5 and the adjacent cavity constituting thehole l and slot 8 but nearer the cathode I5, a metal strip 20 is set,parallel the axis, into the block bounding the cylindrical hole 3 andextends radially to within a short distance of the cathode electrode II;the strip 20 constitutes an electron barrier preventing electrons fromre-passing the flnger I0.

An input lead 21 so the finger H] is sealed through the cylindrical wallof the block by a metal-toglass thimble seal 22, and an output lead 23,terminating in a loop lying within one of the holes 5, is sealed throughalle wall by a metal-to-glass thimble seal 24.

The resonant cavities formed by the holes 5 and slots 6 constitute theresonant output circuits adapted to be excited by electr0ns moving roundthe electron orbit space 3, and Ehe metal tongues formed betweenadjacent slots are connecoed together, a1; each face of the block, bymetal modespacing straps 25, 26, sei: into circular slots formed in thetongues, of which on one face of the block strap 25 connects togetherthe odd numbered tongues, that is to say the first, t'nird, fifth,seventh and nlnth tongues, and strap 26 connects together the evennumbered. tongues, that is to say the second, fourth, sixth and eighthtongues, counting round the block, whilst on the other face of the blockthe outer strap 25 connects the second, fourth, sixth and eighth tongueswhilst the inner strap 26 connects the first, third, fifth, seventh andninth tongues. The spacing between the resonant output caviales isarranged relative to the electro static and magnetic fi8lds 130 be usedto correspond to the mean velooity of the electrons round the electronorbit space so that the distance between successlve resonators is halfthe length occupied by a complete cycle of electron density variation.

T0 each face of the shallow recess from Which the fianges 2 project isscrevved. a potentialequalising platze 29 and the block ls sealed off bymeans of end-plates 21 attached to the fiange 2 in accordance with theusual magnetron technique.

The apparatus is evacuated and finally sealed oft by means of a pumpinglpube 28 sealed to the glass thimble of one of the cathode electroolelead seals.

For amplification of an input oscillation of frequency 3000 megacyclesper second with apparatus relatively dimensioned as shown, the radius ofthe block I should be about two inches.

I claim:

1. A magnetron device comprising an anode electrode and a parallelcathode electrode defining between them an ended electron Orbit space,means for producing a stream of electrons originating ab one end of saidspace ancl flowing along the space, means for receiving a high frequencyinput osclllation, means for density modulating said electron stream atsaicl end of saicl space in accorclance with the amplitude and frequencyof the input oscillation, a plurality of resonant output circuitsconnected across slots formed in said anode electrode and spaced apartalong said electron o1bit space so that said circuits are excitable insuccession by said density modulated stream of eleotrons and resonant asa whole a1: a frequency n f, where n is an integral number and f is thefrequency of said input oscillation, and means for extracting therequired output oscillation from said output circuits.

2. A magnetron device as sei: forth in claim 1 which functions as anamplifier wherein n equals one.

3. A magnetron device as sei; forth in claim 1 which functions as afrequency multiplier Wherein n is an integer greater than one.

4. A magnetron clevice comprising a metal block anode electrode and aparallel cathode electrode defining between them an ended electron orbitspace through which electrons can flow under the influence of anelectric field applied between said electrodes and a transverse magneticfield, said anode block being recessed at one region 120 form an inputcavity system resonant ab frequency f and ab another region well spacedalong the electron orbit space from said first region being recessed toform a plurality of mutually coupleol resonant cavities arranged insuccession along the electron orbit space to form an output cavitysystem resonant at frequency n f, where n is an integral number, athermiom'c cathode whose electron emissive surface occupies a restrictedregion of said cathode electrode lying opposite said input cavitysystem, input means for applying an input oscillation to excite saidinput cavity system at frequency for controlling the flow 01 electronsfrom said cathode, and entput means for extracting from said outputcavity system oscillations of frequency n f excited by the fiow ofelectrons through said (alectron orbit space.

5. A magnetron devica comprising a cylindrical cathode electrodecontaining a thermionic cathode whose electron emitting surface extendsaxially along the cathode electrode surface but occupies only a smal1circumferential width thereof, a cylindrical metal block anodeelectroole lying concentric With but spaced from the cathode electrodeoo form between them the magnetron electron orbit space, at least ones1ot extending axially through the anode block at a region thereofopposite said electron emissive surface to form an input cavity systemresonant a1: a frequency f for controlling the emission of electronsfrom said cathode, a plurality of adjacent slots each extending axiallythrough the anode block over a restricted region thereof well spacedangularly from the input cavity system to form an output cavity systemexeitable by electrons fiowing from the saiol cathode through theelectron orbit space under the infiuence of a radial electric fieldbetween the anode and cathode electrodes anal an axial magnetic fieldand resonant at frequency n f, where n is an integral number, anelectron barrier electroole extending radially between said anode andcathode electrodes at a region between said input and output cavitysystems for preventing repeated circulation of electrons round saidelectron orbit space, input coupling means for excioing said. inputcavity system a1: frequency f, and output coupling means for extractingan output 0scillation of frequency n f from said output cavity system.

6. A magnetron device according claim 5 wherein the slots in the outputcavity system define metal tongues, and wherein said tongues areconnected together on each side of the block by two conductive modespacing straps of which one strap connects together the odd nurnberedtongues and the other connects together the even numbered tongues,counting around the anode block.

WILLIAM ERNEST WILLSI-IAW.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNII'ED STATES PATENTS Number Name Date 2411953 Brown Dec. 3, 19462,412772 Hansell Dec. 17, 1946 2412824 McArthur Dec. 17, 1946 2414085Hartman Jan. 17, 1947 2416298 Fisk Feb. 25, 1947 2418117 Hale et a1.Apr. 1, 1947 2423716 McArthur July 8, 1947 2429291 Okress Oct. 21, 19472437279 Spencer Mar. 9, 1948 2487656 Kilgore Nov. 8, 1949

